1. Field of the Invention
This invention relates generally to printers and, more particularly, to an apparatus for controlling the movement of selected paper-holding trays to feed an electrophotographic printer.
2. Description of the Related Art Printers, such as electrophotographic and laser printers, are typically used in an office environment where they are connected to personal computers, personal computer networks or dedicated word processing computers. Most laser printers used in offices share common advantageous characteristics: small size, high quality print, quiet operation, and adequate speed for most applications.
Laser printers include paper handling mechanisms that usually employ separate trays for holding different types or different sizes of paper. These trays are typically configured to hold approximately 250 sheets of paper. If the paper handling mechanism of a laser printer includes only one tray, then the laser printer is capable of withdrawing paper from only the one tray during a requested printing operation. When the printer receives instructions to print on different types of paper during a print request, the single tray must be removed and replaced with a tray containing the proper paper.
To obviate this problem, laser printers have been adapted to include multiple trays from which different types or different sizes of paper may be withdrawn. When a multiple-tray printer receives instructions to print on different type of paper during a print request, the paper handling mechanism associated with the printer simply withdraws paper from the appropriate tray.
A paper feeding mechanism is used to withdraw paper from a tray, and typically includes at least one rubber-like roller that rotatably engages the paper within the tray and draws the paper into the printing mechanism. When a laser printer includes a paper handling mechanism that includes more than one tray, each tray ordinarily has a dedicated paper feeding mechanism associated therewith. Further, the trays and their associated paper feeding mechanisms are normally stacked in a vertical arrangement, and, therefore, consume vertical space equal to the vertical height of each 250 sheet tray and the vertical height of each paper feeding mechanism. Accordingly, the combined vertical height of each tray and paper feeding mechanism limits the maximum number of trays that can be associated with a paper handling mechanism of a laser printer.
Since commonly used paper trays include a spring which forces the paper within the tray into contact with the rubber-like roller of its associated paper feeding mechanism, the pressure between the paper picker and the stack of paper varies with the thickness of the stack of paper remaining in the tray. The paper feeding mechanism is stationary, so that the spring force applied to the stack of paper constantly maintains the top sheet of paper in contact with the paper feeding mechanism. Thus, when it is desired that additional paper be loaded into a particular tray, the printing process from that tray must cease while the tray is removed and the paper supply replenished. This is particularly important where the user wishes to print a short run of unique paper that differs from the paper currently loaded in the tray.
Previous laser printers have employed a single sheet feeding mechanism whereby an operator desiring to print a small number of copies on a paper style unique from that currently loaded in the trays may singularly and consecutively feed the number of sheets required for the printing process. This, of course, is a time intensive process that does not free the user to accomplish other tasks, but requires that the user remain at the printing station, consecutively feeding each sheet of paper into the printer, until the entire printing process is complete.
Alternatively, the user may remove the tray from the paper handling mechanism, insert the desired number of pieces of paper into the tray and replace the tray in the paper handling cassette. While this method does free the user to leave the area of the printer during the printing process, the procedure of removing the tray and loading the tray with a precise preselected number of unique sheets of paper causes the printer to discontinue printing until the tray has been replaced.
The present invention is directed to overcoming or at least minimizing one or more of the problems as set forth above.